1. Field of the Invention
The invention relates to a brushless DC motor.
2. Description of the Related Art
Magnetic materials used in a rotor iron core of a high performance brushless DC motor are divided into two categories: one is weak magnetic ferrite or bonded rubidium iron boron while the other one is sintered rubidium iron boron made of strong magnetic materials. Disadvantages of above materials are as follows: 1) when weak magnetic ferrite or bonded rubidium iron boron are used in a rotor iron core, the motors, often having a Hall element and a magnetic ring inside, will have a large volume and consume large amounts of copper and iron. The cost will be relatively high; 2) when sintered rubidium iron boron made of strong magnetic materials are used for a rotor iron core, the magnetism will be extremely strong; if a Hall element and a magnetic ring are arranged inside a motor casing, the Hall element will suffer from great interference when sensing signals. Thus, the measurement accuracy will be affected leading to inaccurate or even unsuccessful control.
To solve above problems, some motor manufacturers arrange the Hall element and the magnetic ring outside the motor end cover, but following problems still exist: mounting structure layout of the Hall element and the magnetic ring is not reasonable, installation is unfriendly, reliability is poor, and cost is high.